The present invention relates to a four-stroke cycle internal combustion engine, in which oil mist is generated in the vicinity of a crank chamber and the generated oil mist is fed from the crank chamber to a valve chamber through an oil-mist passage so as to lubricate internal mechanisms in the crank chamber and the valve chamber, and more particularly to a four-stroke cycle internal combustion engine having an oil-mist breather.
It has been known in a conventional four-stroke cycle internal combustion engine to generate oil mist in the vicinity of a crank chamber. The generated oil mist is fed from the crank chamber to a valve chamber through an oil-mist passage so as to lubricate internal mechanisms in the crank and the valve chambers. In such a four-stroke cycle internal combustion engine, an oil reservoir chamber is typically provided below the crank chamber to accommodate lubrication oil therein. The lubrication oil reserved in the oil reservoir chamber is atomized or formed into an oil mist, for example, by splattering the lubrication oil by an oil dipper provided at the lower end of a connecting rod or by agitating the lubrication oil with a coil spring. The oil-mist passage is formed in a cylinder block of the engine to provide fluid communication between the crank chamber and the valve chamber, so that the oil mist is fed from the crank chamber to the valve chamber through the oil-mist passage by a force of a positive pressure in the crank chamber during a downward movement of a piston of the engine. The oil mist fed into the valve chamber lubricates a valve mechanism in the valve chamber, and the remaining oil mist is discharged from an oil-mist breather.
In the conventional four-stroke cycle internal combustion engine, the oil-mist breather is generally disposed in the vicinity of an inlet of an air intake system, and an air filter is also disposed in the vicinity of the inlet of the air intake system. Thus, the oil mist discharged from the oil-mist breather is sucked through the air filter together with outside air, and part of the oil mist is trapped by the air filter. The trapped oil mist or lubrication oil undesirably accelerates contamination of the air filter, resulting in reduced intake air flow.
It is therefore an object of the present invention to provide a four-stroke cycle internal combustion engine having an oil-mist breather free from the defect causing contamination of the air filter.
In order to achieve the above object, the present invention provides a four-stroke cycle internal combustion engine in which lubrication oil is atomized to generate oil mist so as to lubricate an internal mechanism of the engine with the oil mist. The four-stroke cycle internal combustion engine includes an oil-mist breather in fluid communication with a fuel tank of the engine. The oil mist remaining after lubrication of the internal mechanism is discharged into the fuel tank through the oil-mist breather.
In the four-stroke cycle internal combustion engine of the present invention, an air which contains oil mist remaining after the lubrication of the internal mechanism is discharged into the fuel tank through the oil-mist breather, and the air which contains the oil-mist discharged from the oil-mist breather acts to compensate all or a part of the reduced volume in the fuel tank caused by pumping fuel out of the fuel tank. If the air containing the oil-mist from the oil-mist breather is insufficient to compensate the reduced volume in the fuel tank, a fuel-tank breather may be provided to bring additional outside air into the fuel tank therethrough so as to supplement the insufficient quantity. The discharged lubricating oil into the fuel tank is mixed with the fuel in the fuel tank, and then burnt in a combustion chamber of the engine together with the fuel. Even if some lubricating oil is contained in the fuel, the four-stroke cycle internal combustion engine does not receive any adverse effect in its performance.
As above, the air containing the oil mist remaining after lubrication of the internal mechanism is discharged into the fuel tank. Thus, the four-stroke cycle internal combustion engine of the present invention eliminates the conventional problem that the air filter provided at the inlet of the intake system is contaminated by the lubricating oil thereby preventing the air filter from reducing intake air flow. Thus, surroundings of the engine is free from contamination from the lubricating oil.
Further, the present invention provides a four-stroke cycle internal combustion engine in which oil mist is generated in the vicinity of a crank chamber and the generated oil mist is fed from the crank chamber to a valve chamber through an oil-mist passage so as to lubricate the inside of the crank camber and the valve chamber. The four-stroke cycle internal combustion engine includes an oil-mist breather including a breather passage for providing fluid communication between the valve chamber and the fuel tank. In this case, the remaining oil mist in the valve chamber is discharged into the fuel tank through the oil-mist breather.
In this four-stroke cycle internal combustion engine of the present invention, an air containing the oil mist remaining after the lubrication of respective internal mechanisms of the crank chamber and the valve chamber is discharged into the fuel tank through the oil-mist breather. The discharged lubricating oil is mixed with a fuel in the fuel tank, and then burnt in a combustion chamber of the engine together with the fuel.
Thus, the four-stroke cycle internal combustion engine of the present invention eliminates the conventional defect in that the air filter provided at the inlet of the intake system is contaminated by the lubricating oil thereby preventing the air filter from reducing intake air flow. Surroundings of the engine are free from contamination due to the lubricating oil.
In one specific embodiment of the present invention, the oil-mist breather may include a check valve disposed in the breather passage and an orifice disposed in the breather passage on the upstream side of the check valve. The check valve is operable to close the breather passage when a fuel in the fuel tank flows into the breather passage and when a piston of the engine is moving upward.
In the above embodiment, the orifice and the check valve may be disposed in the vicinity of the fuel tank along the longitudinal direction of the breather passage.
Further, in the above embodiment, the check valve may be disposed closer to the fuel tank than the orifice, and the check valve may include a valve member for closing an outlet of the orifice on the side of the fuel tank.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description.